Removing solvents from plastic colloids



l atented Got. 16, 1 934 llNl'lEfi STATES REMOVING SOLVENTS FRGM PLASTICCQLLOIDS Harry P. Bassett, Cynthiana,'ly.

No Drawing. Application .lune 26, 1931, Serial No. 547,191

7 Ulaims. (Cl. 18-51 This invention relates to a process of removingsolvents from semi-solid or plastic colloids and in its specificembodiment relates particularly to the removal oi solvents fromcellulose nitrate plastic compositions such as celluloid.

The principal object of this invention is to provide a simole andeiilcient process of removing solvents from plastic colloids whereby aproduct or superior quality is obtained and the r 10 moval of solventsis accomplished in a relatively short period as compared with the timerequired in similar processes heretofore generally employed.

An important object of this invention is to provide a simple, rapid andefficient process of removing solvents from nitro-cotton or similarplastic compositions which is substantially free from the disadvantagescommonly encountered in the proce heretofore generally employed forsimilar purposes.

A further object of this invention is to provide improved process ofpreparing celluloid or other plastic sheets which are particularlyadapted for use in rnaiiin shatter-proof glass.

Other objects and advantages of the invention will become apparentduring the course or" the following description. 7

I have discovered a simple process for removsolvents from freshly formedor partially finished plastic colloids such as vulcanized fiber,

celluloid, and the like, which process not only is particularlyeffective in removing the solvents but produces finished products ofsuperior qualities and appearance. While, as suggested, the

process is applicable for use for removing solvents such as zincchloride from plastic compositions such as vulcanized fiber, theinvention is particularly adapted for application in the removal ofsolvents from cellulose nitrate plastic.

compositions, particularly celluloid. The process is based on mydiscovery that solvents may be removed from plastic colloids Withoutharm to the quality or color of the final product by exposing suchcolloids to an atmosphere of the vapor of a nonsolvent of the colloidwhich is miscible with the solvent in the colloid and thereafter heatingthe colloid in a dryer at gradually increasing temperatures between theapproximate limits of 100 F. and 160 F. In the preferred practice of theprocess the vapor bath or atmosphere to which the colloid is initiallyexposed contains a major proportion of the solvent-miscible nonsolventof the colloid, the concentration of which in the atmosphere is reducedduring the process, the heating of the eierrcd to being of e concen-"old and becolloid in started a; tration as the nonsolve is mi ciblewith the solven cordingly, in preferred p iy formed or partially leplastic colloid to be treated to the action or an tinosphere of watervapor. While the per entage of the water vapor present in the vapor bathatmosphere may be varied to a considerable extent, i found that iiproved results are obtained if the water vapor is in such an: cunt thatthe relat midity oi the atmosphere 1 the v no bath is about andpreferably in the neighborhood of "26%. While various vapors or gasesmay be employed the di ing factor in the vapor bath, air is the obviousa fluid to be employed for this purpose and c.nce fully satisfactoryresults are obtaine when air is employed, I recommend its use. Thus, inpreferred practice the plastic colloid im ally subjected to a vapor bathof air and water vapor, relative humidity in which atmosphere is above75% and preferably about 75% After subjecting the colic 1 cc, 1 subjecta fresh- 5 1 b0 such an atmosphere for from several hours to se eraldays, depending upon the nature, size, thickness, etc. of the colloidunder treatment, the concentration of the water vapor in the bath ispreferably reduced so that the relative humidity of the resulting amosphere is materially lowered, say to 40%. Thereafter, the contentwater vapor is lowered ag in, preferably to such an extent that theresuiting atmosphere will have relative humidity of about 15%. Ofcourse, the lowering of humidity may be more gradual than justindicated, if

desired, but I have found that a more gradual reduction in theconcentration of water vapor in the atmosphere is not necessary generalpractice. Either after the original humidity of the vapor bath has beenlowered, to say. about 46%, 1 or after the reduction or" the to thelowest point to which it is to be lowered (or at any intermediate point,for that matter), the colloid is heated to a temperature of say 160 F.and the temperature is gradually raised, over a period of from severalhours to several days, to a more elevated temperature which ordinarilyshould not exceed 160 F. As stated above, the temperature is graduallyincreased as the humidity of the vapor bath is gradually decreased.After the atmosphere for about five days.

completion of this treatment it will be found that the solvents presentin the colloids are substan tially removed and the products are incondition for general use.

Whereas, in accordance with the preferred embodiment of the invention,solvent is to be removed from cellulose ester colloids, the freshlyformed articles which may be obtained either by slicing a block of thepartially finished plastic colloid or by extruding a plastic colloidmix, are suspended in a chamber which may conveniently be a dryingchamber of conventional type for ageing or seasoning plastic colloidarticles. In the initial stage of the process the vapor treating bath isintroduced into the drier preferably by causing water vapor to enterfrom the bottom of the drier together with air. The drier should beprovided with an outlet at the top so that there will be a current ofthe treating vapor through the drier. I have found it convenient toemploy a cold water spray at the inlet of the drier which may becontrolled to regulate the humidity in the drier. As stated above, Iprefer that the atmosphere to which the freshly formed plastic colloidsare initially exposed shall have a relative humidity preferably inexcess of and, for best commercial practice under ordinary conditions,about 76%. The temperature of the atmosphere in the initial treatment ofthe articles may advantageously be normal atmospheric temperature. Suchan atmosphere may be used for all thicknesses of articles in the initialtreatment but the time of treatment with this atmosphere will be variedaccording to the particular thickness of article. For example, in thecase of a plastic colloid article having a gauge of 215, I prefer toleave the article in this On the sixth day the humidity in the drier ispreferably reduced to about 40% and heated air is introduced into thedrier so that the temperature therein will be approximately from to 104F. On the seventh day, the humidity is dropped to about 15% and thetemperature in the drier is raised to about F. Thereafter, thetemperature is raised gradually to F. for the eighth day, to F. for theninth day, and to F. for the tenth and eleventh days. At the end of thistime, the stock is fully aged and ready to be used.

As is apparent from the foregoing, a treatment for eleven days issuflicient for relatively thick celluloid articles. As articles oflesser thickness are treated, the time of treatment may becorrespondingly decreased. For example, with a 60 gauge plastic colloidarticle, I have found that complete ageing is obtained by treatment forapproximately one day in a vapor bath of the characteristics set forthabove at ordinary temperature, followed by a treatment for about twelvehours at reduced humidity and a temperature of 100 F., subsequenttreatment for twelve hours at 130 F., with treatment for one day at 160F. as a final step. Of course, the increase in temperature is preferablygradual and the decrease in humidity of the vapor bath is likewisegradual. However, some satisfactory measure of success may be obtainedby initially reducing the humidity to the minimum degree of humidityemployed followed by the gradually increasing heat treatment.

- While I have described in detail the preferred practice of my processit is to be understood that ,the details of procedure, such as the timeof treatment, the vapor bath employed, and the concentration of treatingagent in the vapor bath, may be variously modified without departingfrom the spirit of the invention or the scope of the subjoined claims.

I claim:

l. The process of removing solvent from a cellulose ester plasticcomposi same and containing pla comprises treating such cello of watervapor, thereafter heating the colloid at gradually increasing temp tweenthe approximate lim F., and gradually reducing the water vapor in theatmosphere surroun ing said colloid during said heating.

2. The process of removing solvent from a cellulose ester plasticcompotion containing the same and containing a plasticising agent whichcomprises exposing such colloid to atmosphere of water vapor, therelative humidity of which is above '70, thereafter heating the thustreated colloid at gradually increasing temperatures be tween theapproximate limits of 100 F. and 160 F., and gradually reducing theconcentration of water vapor in the atmosphere surrounding said colloidduring said heating.

3. The process of removing solvent from a cellulose ester plasticcomposition containing the same and containing a plasticizing agentwhich comprises exposing such colloid to an atmosph of water vapor, therelative humidity of w o. is above 70, gradually reducing the humidityof atmosphere and, while the humidity is being reduced, heating thecolloid at gradualiy increasing temperatures'between the approximatelimits of 100 F. and 160 F.

4. The process of removing solvent from a cellulose ester plasticcomposition containing the same and containing a plasticising agentwhich comprises exposing such colloid to an atmosphere of water vapor, t-e relative humidity of which is approximately 76, gradually reducingthe humidity and simultaneously heating the colloid at graduallyincreasing temperatures between the approximate limits of 100 F. and 160F. k

5. The process of removing freshly formed cellulose nitrate plasticcomposition which comprises treating such composition with a bath ofwater vapor, thereafter heating t e composition at gradually increasingtemperatures between the approximate limits of 100 F. and 160 F., andgradually reducing the concentration of Water vapor in the atmospheresurrounding said composition during said heating.

6. The process of removing solvent from a freshly formed cellulosenitrate plastic composition which comprises exposing such composition toan atmosphere of water vapor, the relative humidity of which is above'70, and reducing the humidity of said atmosphere and heating thecoinposition at gradually increasing temperatures between theapproximate limits of 100 F. and 160 F.

'7. The process of seasoning .eshly formed cellulose ester plasticcomposition sheets contr 'ng a solvent and plasticizing agent which cornwoes solvent from a exposing such sheets for a period of from severalhours to several days to an atmosphere of w te vapor, the relativehumidity of wla proximately 76%, gradually reducing the hum saidatmosphere, and heating the sheets over a period of several days atgradually increasing temperatures between the approximate limit 100 F.and 160 F.

HARRY P. BASSETT.

